There are interactive displays which comprise a projector or a Liquid Crystal Display panel to form an image on a surface, a camera behind the surface and computer vision circuitry for detecting user input.
US 2001/0012001 A1 discloses one such display system. This system comprises a semi-transparent screen and an infrared LED (light emitting diode) panel, a CCD (charge coupled device) camera and a projector provided on the back side of the semitransparent screen. The camera operates on infrared wavelengths and detects infrared light reflected from objects on the other side of the semitransparent screen, when the objects are relatively close to the screen or when they touch the screen. The projector projects visible image light onto the screen. Infrared component of the image projected by the projector may be filtered out. Thereby the projected image does not disturb the camera.
ACM publication “ThinSight: Integrated Optical Multi-touch Sensing through Thin Form-factor Displays” by Izadi et al. discloses another type of interactive displays.
In this publication individual infrared emitter/detector pairs placed behind backlight of an LCD (liquid crystal display) display are used to detect objects on or in the vicinity of the LCD display, the LCD display thus operating as an interactive display. The use of an LCD display may overcome many of the problems of the projector-based interactive screens. The disclosed technology however requires number of infrared emitter/detector pairs to be mounted on the system, if input is to be detected on a larger area, whereby production of such interactive displays is laborious and thus high costs may be involved.
In the absence of ambient IR light, the display may illuminate objects on or near its surface by means of IR illumination, but it is very difficult to counter excessive ambient IR illumination. Detecting an object on the surface of the display with an IR camera is complicated by the presence of sunshine or other strongly IR-emitting illuminators such as halogen lamps. Namely, in this case the infrared-emission that the system produces may not be strong enough to cause near-by objects to appear as highlights. For instance, one known technology for detecting a finger touching the display surface is to detect when an image of the finger becomes crisp. A diffusive screen is attached onto the display surface so that a touching finger blocks IR light from being diffused by the diffusive screen under the finger and a relatively sharp shadow is formed conforming to the shape of the contact. However, under strong, coherent light such as sunshine, any object casts a sharp shadow on the camera even from a distance. Hence, it may be impossible to detect a contact simply from the sharpness of the shadow. Moreover, under strong ambient IR light the camera signal may be flushed with measured light such that it is generally impossible or at least very difficult to distinguish any meaningful picture.
US20080062123A1 discloses an interactive video display system. According to the abstract, the system uses strobing light to allow easy and unencumbered interaction between a person and projected video images. A camera may be synchronized to the strobing light and the strobing light may be in an infrared spectral range. A processing system detects images of a human in the field of view of the camera and controls the display so that the projected video images are changed based on an interaction between the human and the projected video images. The system may project the video images on a surface around the person and may move the projected video images on the surface based on a movement of the person. The projected video images may include computer-generated characters and/or virtual objects that react to the movement of a person.
U.S. Pat. No. 6,339,748B1 discloses in its abstract an object to provide a coordinate input system imparting a coordinate input function onto a transmissive screen for image display such as a rear projecting display apparatus, which permits use of a ray reflecting indicator smaller in size and lighter in weight than a light pen and to improve easiness to use. The coordinate input system of the invention has an infrared ray source 3 which projects an infrared ray onto the back surface of the transmissive screen 2 for image display, a CCD camera 4 which covers the back surface of the transmissive screen as a senses range, and an image information processing circuit 5 which generates coordinate information of a ray reflecting indicator 1 located in front of the transmissive screen 2, from output image information of the CCD camera.
It is an object of the present invention to avoid problems associated with prior art and/or to provide an alternative to existing technology.